EP0324582A2 - Verfahren zum Messen der Zeit zwischen Pulsen - Google Patents

Verfahren zum Messen der Zeit zwischen Pulsen Download PDF

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Publication number
EP0324582A2
EP0324582A2 EP89300187A EP89300187A EP0324582A2 EP 0324582 A2 EP0324582 A2 EP 0324582A2 EP 89300187 A EP89300187 A EP 89300187A EP 89300187 A EP89300187 A EP 89300187A EP 0324582 A2 EP0324582 A2 EP 0324582A2
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EP
European Patent Office
Prior art keywords
pulse
radiation
light
primary
flight
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP89300187A
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English (en)
French (fr)
Other versions
EP0324582A3 (de
Inventor
Andrew Ian Grant
Martyn Taylor Macpherson
David Graham Stevens
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BP PLC
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BP PLC
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Filing date
Publication date
Application filed by BP PLC filed Critical BP PLC
Publication of EP0324582A2 publication Critical patent/EP0324582A2/de
Publication of EP0324582A3 publication Critical patent/EP0324582A3/de
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S17/14—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters

Definitions

  • This invention relates to an improved method for determining the effective distance from a light generating and detecting system situated on a moving airborne platform to a target at or near ground or sea level for optical remote sensing and other applications.
  • This method will be significant for remotely sensed light scattering, laser-induced fluorescence, and differential light absorption measurements from moving platforms.
  • Minerals may be exposed by weathering to produce anomalous regions or they may become a surface expression of the underlying materials through migration from the subsurface.
  • a particularly important example of the latter is the natural seepage of hydrocarbons from subterranean reservoirs which may be either on or offshore.
  • Offshore petroleum exploration technology especially the use of reflection seismic, has developed to the extent that the structure and thickness of potentially oil-bearing rocks can be determined with a degree of confidence which is limited mostly by cost.
  • many areas still have either widely scattered wells or no wells at all, and in such places geochemical information may be insufficient to determine whether petroleum has been generated and its subsequent history.
  • Detector systems frequently involve the use of pulse gating and this requires accurate altitude determination for detector timing and synchronisation and subsequent correction of detected optical signal returns for altitude variations.
  • Timing and synchronisation accuracy for optical detector means employing radar altimetry may be as poor as ⁇ 200 nanoseconds, equivalent to an accuracy of the radar altimeter of ⁇ 100 ft for the absolute detector to target distance under high pitch and roll conditions.
  • a method for determining the total time of flight distance of a light pulse from a generator on a moving airborne platform, such as an aeroplane, to a target, which may be topographic at ground or sea level which method comprises the steps of triggering a pulse of primary light radiation from the generator towards a surface at or near ground or sea level, the beam being sufficiently intense and of such spectral composition that the beam causes the surface to absorb some light radiation, detecting the secondary light emission or the reflected primary radiation backscatter and using the outgoing primary light radiation and the returning secondary radiation or the reflected primary radiation to operate triggers on the start and stop inputs of a timer to determine the time of flight of the light pulse from the airborne platform to the target and back again and using the total time of flight distances to determine the timing synchronisation for the opening of the shutter or the detector gating for the subsequent pulse before the return of that pulse of induced secondary radiation or reflected primary radiation, and thus, to circumvent the minimum propagation delay in the electronic circuitry.
  • the pulse of primary light radiation is preferably a pulse of laser light, most preferably ultra-violet light, which may be generated by an excimer laser.
  • Suitable sources include a metal gas discharge laser, a flash-pumped laser or a semi-conductor pumped solid-state laser.
  • lasers may be Nd-YAG lasers, ruby lasers or pulsed argon ion lasers.
  • the pulsed lasers may have nanosecond or picosecond pulse widths.
  • the picosecond pulsed lasers may comprise a source laser, a synchronously pumped, cavity dumped, dye laser with amplifiers and further wavelength shifting units. It is envisaged that regenerative amplification systems with high repetition rate may be included in the picosecond source of laser radiation.
  • the secondary light backscatter or reflected light backscatter is preferably collected by an optical telescope.
  • This method permits accurate interrogation of signals emanating from above, below or at the target distance, as required, by synchronising precisely the detector shutter or detector gating over the relevant returning optical signals.
  • a reference level e.g. the surface of the sea
  • the precise altitude or source distance may be established for the purposes of accurate time-domain "box car” detector gating and synchronisation, or similar, and also accurate altitude or source distance for signal normalisation.
  • the invention relies upon H (N-1) being a good measure for H (N) .
  • the invention stores the true H (N) for subsequent use in data processing and carries its value forward in turn in the circuitry to determine the timing for H (N+1) .
  • the technique is particularly applicable to the software configurable, high spectral and digital resolution, airborne optical detector system for the detection of radiation over the UV to the red wave band and beyond, disclosed in our copending British patent application no. 8800583 (BP Case No 6874).
  • This application discloses apparatus for detecting an anomaly at or near a water or land surface
  • apparatus comprises means for generating a beam, preferably a pulsed beam, of primary light radiation, preferably ultra-violet light, and directing the beam towards the surface, the beam being sufficiently intense and of such a spectral composition that the beam causes the anomaly, if present, to emit secondary light radiation, means for collecting the secondary light radiation or means for collecting solar induced secondary light radiation, spectral analysis means for analysing the spectrum of the emitted secondary radiation, and a high resolution, multi-element digitising detector for receiving the analysed secondary radiation, having a plurality of channels across the spectrum of the emitted secondary radiation, the channels being software configurable and under the control of a digitally addressable computer-operated controller, the concentration of used channels across the plurality of channels being adjustable and increasable in the regions of the spectrum of greatest interest and decreasable in the regions of least interest.
  • Figure 1 is a diagrammatic representation of an airborne laser fluorosensing system
  • Figure 2 shows the detector of Figure 1 fitted with a pulse timing system according to the present invention
  • Figure 3 is a timing diagram.
  • the system is fitted within the interior of a light aircraft 1. It comprises an excimer laser 2 emitting a pulsed beam 3 of primary ultra-violet light radiation which is reflected by a mirror 4 through a port 5 in the underside of the aircraft and directed downwardly to the surface of the sea 6.
  • Rays of secondary light radiation 7 induced by the primary beam are collected by a reflecting telescope 8, further reflected by the mirror 4 and passed through a grating spectrograph 9 which disperses the light onto a gateable optical multi-channel detector 10 which is software configurable and capable of multi-element digitising to 512, 1024 or more channels, although only a selection may be used in practice.
  • signals are passed to a digitally addressable software configurable controller 11 which controls the effective digitisation across the multi-element detector.
  • Data is logged, displayed and stored by logger 12, display unit 13 and store 14.
  • the timing and synchronisation circuitry operates in this preferred form of the invention as follows. From an optical trigger unit 20 driven from a master clock in the timing and synchronisation circuitry 21 a trigger pulse A is sent to the laser trigger unit 22 causing the laser 2 to discharge a laser pulse B. Part of this laser light pulse is split off by the beam splitter 23 to fall onto a fast photodiode photodetector 24, and by trigger unit 25, send a trigger pulse C to a fast counter 26. The photodetector 24 also sends an energy reading to the controller 11 through the ADC 30. Synchronous with the laser pulse B, a pulse trigger C is generated. This starts the fast counter 26 based on a clock with sufficient time resolution to discriminate heights with the required accuracy.
  • Counter 26 contains a 200 MegaHertz clock which will provide 5 nanoseconds timing resolution equivalent to an airborne platform to signal source distance determination accuracy of ⁇ 2.5 feet.
  • the laser beam B goes on to the sea or land surface by a retroreflector 4 which is part of the receiving optics, containing a telescope 8.
  • the collected radiation D contains excited luminescences from the target and reflected primary radiation.
  • the unchanged reflected primary radiation is split off by a dichroic beamsplitter 27 to form beam E.
  • Beam E may alternatively comprise a portion split off from the returning primary and secondary radiation. Beam E falls onto a fast photodiode photodetector 28, to generate by means of trigger unit 29 a pulse F to stop the counter 26.
  • the laser beam has left the airborne platform, hit the target and reflected primary radiation and secondary radiation has returned to the receiving system, and a round trip time for the laser light pulse has been established in counter 26.
  • the speed of light is known, approx. 2.99 x 108 metres per second, and so an accurate distance between the airborne platform and the signal source, or target, may be established.
  • This value is passed to the controller 11 and subsequently to the data logger 12 for storage and use in data analysis. More importantly this value is also passed to the timing and synchronisation circuiting 21 for the next pulse of primary radiation as shown in Figure 3.
  • the laser trigger pulse A is initiated for every other pulse of the master clock CLK, the timing and synchronisation circuitry (21 of Figure 2).
  • Counter Start C is generated with the laser pulse B of Figure 2 but may not be precisely simultaneous with A because of propagation delays in the laser electronics.
  • C determines the time zero for the particular laser pulse e. g. t N-1 zero for the (N-1)th laser pulse.
  • the returning primary and secondary radiation, (D of Figure 2,) generates pulse F Counter Stop which halts the timing counter at the time of flight for the (N-1)th laser pulse.
  • the fast counter, 26 of Figure 2 now reads H (N-1) seconds for the (N-1)th pulse which is a measure of the round trip time for that laser pulse.
  • the High Volt Gate G is the detector, (10 of Figure 2,) gate and must be opened before E is propagated.
  • the position in time for the asterisked Nth High Gate Signal of G is determined from the time zero of the Nth laser pulse t N zero ; the previous pulses' time of flight, H (N-1) and the MPD of the system.
  • t N gate t N zero + H (N-1) - MPD.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)
EP19890300187 1988-01-12 1989-01-10 Verfahren zum Messen der Zeit zwischen Pulsen Withdrawn EP0324582A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB888800584A GB8800584D0 (en) 1988-01-12 1988-01-12 Method of timing pulses
GB8800584 1988-01-12

Publications (2)

Publication Number Publication Date
EP0324582A2 true EP0324582A2 (de) 1989-07-19
EP0324582A3 EP0324582A3 (de) 1990-12-19

Family

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EP19890300187 Withdrawn EP0324582A3 (de) 1988-01-12 1989-01-10 Verfahren zum Messen der Zeit zwischen Pulsen

Country Status (4)

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EP (1) EP0324582A3 (de)
JP (1) JPH01214790A (de)
AU (1) AU2769189A (de)
GB (1) GB8800584D0 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005001407A2 (en) 2003-03-11 2005-01-06 Rosemount Aerospace Inc. Compact laser altimeter system

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8800583D0 (en) * 1988-01-12 1988-03-23 British Petroleum Co Plc Remote sensing system
US5046839A (en) * 1990-07-30 1991-09-10 Locker Enterprises, Inc. Golf course range finder system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2104961A1 (de) * 1970-09-10 1972-04-28 Onera (Off Nat Aerospatiale)
AU505439B2 (en) * 1976-04-30 1979-11-22 Earth Search Inc. Laser prospecting for hydrocarbon seeps
US4334199A (en) * 1978-10-27 1982-06-08 The University Of Rochester Excimer laser

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2104961A1 (de) * 1970-09-10 1972-04-28 Onera (Off Nat Aerospatiale)
AU505439B2 (en) * 1976-04-30 1979-11-22 Earth Search Inc. Laser prospecting for hydrocarbon seeps
US4334199A (en) * 1978-10-27 1982-06-08 The University Of Rochester Excimer laser

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
APPLIED OPTICS, vol. 19, no. 6, March 1980, pages 863-866, New York, US; R.A. O'NEIL et al.: "Field performance of a laser fluorosensor for the detection of oil spills" *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005001407A2 (en) 2003-03-11 2005-01-06 Rosemount Aerospace Inc. Compact laser altimeter system
WO2005001407A3 (en) * 2003-03-11 2005-07-21 Rosemount Aerospace Inc Compact laser altimeter system
US7106424B2 (en) 2003-03-11 2006-09-12 Rosemount Aerospace Inc. Compact laser altimeter system
US7342647B2 (en) 2003-03-11 2008-03-11 Rosemount Aerospace Inc. Compact laser altimeter system

Also Published As

Publication number Publication date
AU2769189A (en) 1989-07-13
EP0324582A3 (de) 1990-12-19
JPH01214790A (ja) 1989-08-29
GB8800584D0 (en) 1988-03-23

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